The present invention relates to internal combustion engines and specifically to an internal combustion engine having a migrating combustion chamber (MCC). More particularly, this invention describes a special cycle and specific features which allow the MCC engine to operate on this cycle as a self supercharged two stroke cycle engine. This cycle will be disclosed including a detailed description of the timed events between the interrelated chambers required to obtain superior performance in terms of power to weight ratio, fuel efficiency and low emissions over its full load range.
The present invention utilizes the basic two stroke cycle mode of operation as taught in the original MCC engine U.S. Pat. No. 3,630,178. In this early patent, a rudimentary self supercharged MCC engine was disclosed. The engine of the present invention incorporates several significant improvements and a more clearly defined cycle of operation to improve its simplicity of operations and improve performance. Since this initial patent was issued, other variants of operation have been incorporated and patented. These variants are described in U.S. Pat. Nos. 4,325,331 and 4,437,437 which teach how the engine operates in a full expansion mode. These patents teach that if the hot, high pressure combustion gases are expanded down to and below atmospheric pressure, the exhaust will be very quiet and cool, and the over expansion process will help reduce the exhaust emissions. Recent data has shown that the emissions from these engines is significantly better than the current two stroke engines which power the small hand held devices such as; weed cutters, blowers and chain saws. However recent emission requirements being mandated by CARB (California Air Resources Board) and the EPA have practically eliminated the possibility of the small two stroke continuing to be used for these applications in its present form.
Accordingly, the present invention describes an advanced supercharged MCC two stroke variant of the original MCC engine patent. This engine possesses superior performance in terms of higher power to weight ratio, low emissions and excellent fuel economy due to several features as disclosed in this invention. These features are addressed as follows.
Non-symmetrical port timing is provided to allow the pumping (supercharging) chamber to achieve a very high volumetric efficiency. Supercharging of the primary combustion chamber is made possible by the 90 degree phase of the pumping chamber and non-symmetrical porting relative to the combustion chamber. These features in combination with precise port timing will provide superior scavenging control to achieve very low emissions. Also, since this engine utilizes a significant boost pressure and limited expansion it will possess a hot exhaust, appropriate for operating a compact catalytic converter. Further, the supercharging feature will decrease the effective friction and surface to volume ratio. Both of these improvements will increase the thermal efficiency. Additional embodiments of this invention utilize a rotary valve in the crankshaft eccentric to provide non-symmetrical timing required for high volumetric efficiency. Other embodiments include non-symmetrical porting arrangement utilizing a separate rotary valve for each pumping chamber, complete dynamic balance provisions and protected fuel injection provisions for even lower emissions capability. Finally, a feature incorporated as an improvement to the mechanism will contribute to longer mechanical longevity. This embodiment uses a sliding support for the center of the combustion chamber member (CCM) which is located between the center of the CCM and the center of the front or rear power blocks. This feature will eliminate all sliding contact between the CCM and center power block. The object is to negate all sliding contact between the two hot surfaces of the inside center power block and the end of the CCM which are directly exposed to the hot combustion. This feature will also simplify the lubrication requirement of the engine.
The small two stroke engines used on hand held tools such as weed cutters, leaf blowers and chain saws are under heavy attack by environmental agencies such as the EPA and CARB due to their enormous exhaust emissions. The primary problem is the ejection of up to 30 percent of the fuel (hydrocarbons) directly out the exhaust port. The impact of this is so serious that some companies are adapting the much cleaner but more expensive four stroke engines to these hand tools in an attempt to comply with the newer clean air regulations. Although the four stroke engine will come much closer to satisfying the emission regulations, the substitution of the four stroke engine will add a significant burden on the operator in terms of a larger, heavier unit. A further disadvantage will be the additional shaking forces associated with the less frequent but stronger power impulses of the four stroke engine to achieve the same power level.
More recent adaptation of the two stroke engine for automobile applications utilize some form of direct fuel injection into the combustion chamber after the exhaust port has closed to keep the fuel from being lost out of the exhaust port as occurs with the two stroke used on the hand tools. Unfortunately, complexity and cost keep the direct injection technique from being implemented into the small two strokes to reduce their emissions to acceptable levels. Even for automotive applications in which add on catalytic converters are required to control emissions, the fuel injected two strokes are still having trouble obtaining the very low emission levels under all load conditions required by the future standards for the automotive applications. Thus, the age old simple two stroke has received a number of complex refinements, too expensive for small applications and quite possible not quite good enough to qualify it as an ultra clean engine for future automotive use.
The MCC engine of the present invention features a supercharged mode of operation utilizing a boost pressure and precisely timed exhaust closing to dramatically enhance its ability to achieve lower emissions over its entire load range resulting in a higher power to weight and size ratio than the fuel injected two stroke.
It is therefore a primary object of this invention to provide a supercharging mode of operation in which fuel injection is not required to achieve the lower emissions standards for small engine application.
Another object of this invention is to obtain superior and complete scavenging of the exhaust products with the added benefit of producing additional pressure from the supercharging to counteract the back pressure of the catalytic converter in expelling the residual exhaust gases out of the combustion chamber and through the converter.
Yet another object of this invention is to improve the volumetric efficiency of this engine by incorporating a rotary valve. A rotary valve will provide non-symmetrical timing of the mixture into the pumping chamber so that a precise opening and closing angle can be selected to achieve the best possible filling of the chamber. A second method of induction timing utilizes two externally driven rotary valves, one for each pumping chamber, to provide even better volumetric efficiency and concurrently to incorporate a means to achieve complete dynamic balance with externally mounted counter weights.
A further object of this invention is to provide a higher thermal efficiency and lower Brake Specific Fuel Consumption (BSFC) due to this advanced cycle of operation. Supercharging results in a smaller engine relative to the standard two stroke engine for the same power output. This results in achieving a lower effective mechanism friction and also a lower effective surface to volume ratio due to the smaller physical size of the engine.
A further object of this invention is to achieve a simpler method of fuel injection after exhaust port closing. This method is incorporated to achieve the ultra low emission levels required for automotive and larger engine applications. A method of protecting the injection hardware from the high combustion temperatures and pressures will also be disclosed in which the engine utilizes the movement of the MCC engine mechanism itself to protect the injection hardware during the combustion and expansion segment of the cycle.
Yet a further objective is the incorporation of an improvement to the mechanism to improve durability and simplify lubrication requirements.
This invention accordingly utilizes the supercharged two stroke variant of the MCC mechanism as initially described in U.S. Pat. No. 3,630,178 as a basis for providing several important improvements developed for the engine which significantly improves its simplicity and performance. It has been found that non-symmetrical timing for interchamber and functional relationships is required to achieve the high performance levels of the currently described invention. Two specific examples of improvements in this regard are the exhaust blow down angle versus its closing angle and the start of induction of mixture into the pumping chamber versus its closing angle. In contrast to the non-symmetrical port timing now found to be desirable, the initial MCC patent provided near symmetrical timing events for both the exhaust and induction functions timing diagrams. This updated cycle of operation which utilizes the non-symmetrical timing for achieving an advanced self supercharged MCC engine will be described in detail.
A first significant improvement is the incorporation of the non-symmetrical port timing for the admission of the fuel mixture into the pumping chamber. It was found thai a simple rotor valve located in the eccentric of the crankshaft provided this degree of control. This non-symmetrical feature allows longer admission of the mixture into the pumping chamber past its bottom dead center (BDC) position than can be provided by the slide port arrangement as disclosed in U.S. Pat. No. 3,630,178. This feature yields a significant improvement in the volumetric efficiency of the pumping chamber and consequently increases the degree of supercharging available resulting in higher power and efficiency and lower emissions. The non-symmetrical porting feature also allows the start of induction to be delayed past top dead center (TDC which is the position of minimum chamber volume) to a point in which the pumping chamber pressure is less than the induction manifold pressure to keep the left over high pressure mixture generated during the high pressure charging of the combustion chamber from blowing back into the induction manifold and consequently back through the carburetor.
A second aspect of this non-symmetrical feature is the incorporation of externally driven rotary valves directly into the center power block to add an even higher degree of performance in terms of further improved volumetric efficiency and also the means to achieve complete dynamic balance of the engine by the incorporation of counterweights to the rotor valve shafts. The dynamic balancing arrangement is similar to the one disclosed in U.S. Pat. No. 4,437,437 FIGS. 59 through 63.
The overall effect of the higher degree of supercharging is to reduce the engine's physical size compared to a crankcase scavenged two stroke engine of the same power. The smaller physical size results in lower equivalent mechanism friction and a smaller equivalent surface to volume ratio.
The standard crankcase scavenged two stroke engine does not offer the self supercharging feature of the MCC engine since it can not continue to pump the fuel mixture into the combustion chamber after the exhaust port closes. It can only displace a volume of mixture approximately equal to the combustion chamber volume above the exhaust ports. The MCC engine's ability to continue pumping mixture into the combustion chamber after the exhaust port closes qualifies it as a true supercharged variant of the MCC engine. The present invention in which non-symmetrical port timing controls the admission of mixture into the pumping chamber to enhance its volumetric efficiency is a significant addition to further enhance the performance of the MCC two stroke engine. The nomenclature assigned to the supercharged variant of the MCC engine is pressurized induction, single expansion or PISE.
A third aspect of the present invention to further improve its fuel economy and reduced its exhaust emissions is the provision of a method to inject fuel into the combustion chamber after the exhaust port closes. Such a provision consists of an injector located in the center power block, in which after injection is completed, is covered by the movement of the CCM to protect it from exposure to the very hot combustion gases. Taking advantage of the normal movement of the CCM by having it cover the fuel dispensing nozzle during the hot, high pressure portion of its movement will simplify the injection hardware since it will not be exposed to the direct high pressure and temperature of combustion.
Yet a fourth aspect of this invention is disclosed to improve durability by incorporating a center slide for the CCM. This feature represents a major improvement in the mechanics of the MCC engine and allows simpler lubrication provisions required for sustained high speed operation.
Accordingly the intent of this invention is to describe a special cycle of operation which can be achieved by a self supercharged MCC two stroke engine. Also, key features will be described which make it possible for this engine to operate on this cycle and to achieve a high degree of performance.